Contribution of Heterotrophic Nitrification to Nitrous Oxide Production in a Long-Term N-Fertilized Arable Black Soil

To understand the contribution of key microbial processes to nitrous oxide (N 2 O) emission in intensively cultivated black soil, laboratory incubation were conducted at 70% water-holding capacity (WHC) and 25 °C, using different gases (air, oxygen, or argon) within the headspace of the incubation chambers to evaluate gas inhibition effects. Arable black soil was sampled from an experimental field that has received urea since October 1979. Nitrification contributed to 57% of total N 2 O emission, of which as much as 67% resulted from heterotrophic nitrification. These data strongly suggest that high soil organic carbon concentrations and low pH values are more favorable to N 2 O production through heterotrophic, rather than autotrophic, nitrification. Nitrous oxide produced by denitrification accounted for 28% of the total N 2 O emission, and the nitrifier denitrification accounted for 15% of the N 2 O emitted from the tested soil. These findings indicate that heterotrophic nitrification was the primary N 2 O production process in the tested soil.